I think that the first and really only priority is to preserve a love of math. I definitely would not sweat the grades (it's 3rd grade) and I would give your DD some say in how she wants to handle things. Let her decide whether to do the EM homework or not. Let her decide whether she wants to slow down and read carefully to pass the Ten Marks assessments or not. For what it is worth, my children tried Ten Marks over the summers and did say that it can be tricky initially because you have to read carefully and answer as requested. They have also tried (mostly through school) various other online programs including Study Island, FirstInMath (MathFirst?), ALEKS, MathHelp, Khan Academy and thought that Ten Marks seem slightly "harder" for a given level.
